(a) Field of the Invention
The present invention relates to a hydraulic pump and, more particularly, to a hydraulic pump which can perform the function of holding shoes only with one shoe-holding member in an appropriate manner.
(b) Description of the Related Art
Generally, when a hydraulic pump is employed for the high-pressure pumping purpose, it is provided with a swash plate having an inclined side, and a plurality of piston each having a shoe. In order to induce high-pressure pumping operation of such a swash plate-based hydraulic pump in an appropriate manner, the shoe of the piston should tightly contact the inclined side of the swash plate. A sue holding mechanism is usually employed for that purpose.
FIG. 7 is a cross sectional view illustrating a swash plate-based hydraulic pump. The hydraulic pump includes a case 58 having a plurality of fluid paths 52 and 54 and a cylinder-shaped groove 56 with a shaft-bearing hole 57, and a shaft 50 inserted into the shaft-bearing hole 57 of the groove 56 such that it can be rotated. A cylinder block 60 is disposed in the groove 56 of the case 58 such that it can be rotated upon receipt of rotational power of the shaft 50. The cylinder block 60 has a plurality of cylinders 62 each with a passing hole 76 for allowing passage of a fluid between the cylinder 62 and each of the fluid paths 52 and 54. A piston 64 is inserted into the cylinder 62 such that it can reciprocate. A swash plate 68 is combined with the case 58 such that it covers an opening portion of the groove 56. The swash plate 68 has a protruded portion 65 with a top side 66 inclined by a predetermined angle.
A shoe 72 is fixed to the piston 64 via a connecting member 74 and moving along the inclined side 66 of the swash plate 68 with the rotation of the cylinder block 60. The connecting member 74 is formed with a ball joint so that the shoe 72 can freely move along the inclined side of the swash plate 68.
A shoe holder 78 is placed around the shoe 72 to stick it to the swash plate 68. A pair of collars 80 are provided within the cylinder block 60 with a predetermined distance, and an elastic member 82 is tensioned between the collars 80. In order to compress the shoe holder 78 against the shoe 72, a barrel member 86 is disposed between the shaft 50 and the shoe holder 78, and a pin member 84 in turn sticks in between the barrel member 86 and the collar 80 close to the barrel member 86.
In the aforementioned hydraulic pump, the pin member 84 receives elastic force from the elastic member 82 and transmits it to the barrel member 86. The barrel member 86 in turn compresses the shoe holder 78 against the inclined side 66 of the swash plate 68. In this way, the shoe 72 sticks to the inclined side 66 of the swash plate 68 and moves along the inclined side 66 with the rotation of the cylinder block 60. At this time, the piston 64 reciprocates within the cylinder 62 of the cylinder block 60.
In this operation, when the shoe 72 moves downward on the inclined side 66, a fluid is introduced into the cylinder 62 through the fluid-input path 52 via the passing hole 76. In contrast, when the shoe 72 moves upward on the inclined side 66, the fluid introduced into the cylinder 62 is discharged through the fluid-output path 54 via the passing hole 76. In this way, the desired hydraulic pressure can be obtained in the hydraulic pump.
However, in the aforementioned shoe holding mechanism, the plurality of shoe holding components including the collars 80, the elastic member 82, the pin member 84, the barrel member 86 and the shoe holder 78 may cause complicated structure, retarded manufacturing time and increased manufacturing cost, resulting in bad production efficiency. For it can be conceived that some of the shoe holding components are not indispensable for holding the shoes.
It is an object of the present invention to provide a hydraulic pump which can effectively perform the function of holding a shoe only with one shoe-holding member.
This and other objects may be achieved by a hydraulic pump with an elastic shoe holder. The hydraulic pump includes a case having a plurality of fluid paths and a cylinder-shaped groove with a shaft-bearing hole. A shaft is inserted into the shaft-bearing hole of the groove such that the shaft is rotated. A cylinder block is disposed in the groove of the case with a plurality of cylinders such that the cylinder block is rotated upon receipt of a rotational power of the shaft. The cylinder block has a barrel-shaped bottom portion surrounding the shaft. A piston is inserted into each of the cylinders such that the piston reciprocates. A swash plate is combined with the case such that the swash plate covers an opening portion of the groove. The swash plate has an inclined side facing the cylinder block. A shoe has a top side, a bottom side and a stepped middle portion. The top side of the shoe is connected to the piston via a connecting member. The bottom side of the shoe contacts the inclined side of the swash plate. The elastic shoe holder is held between the barrel-shaped bottom portion of the cylinder block and the stepped middle portion of the shoe to compress the shoe against the inclined side of the swash plate.
The elastic shoe holder includes a base with a center hole and a rounded inner edge defining the center hole. The barrel-shaped bottom portion of the cylinder block surrounding the shaft is partially inserted into the center hole of the base. The rounded inner edge of the base contacts the barrel-shaped bottom portion of the cylinder block. A plurality of shoe-holding parts are branched from the base while spacing apart from each other with a predetermined distance. Each shoe-holding part has upper and lower flat portions arranged parallel to each other and a bent portion interconnecting the upper and lower flat portions. The upper flat portion of the shoe-holding part is extended from the base to the bent portion, and the lower flat portion of the shoe-holding part is extended from the bent portion toward the base. The upper and lower flat portions of the shoe-holding part have holes one by one with a common central axis. The shoe-holding part is inserted onto the stepped middle portion of the shoe through the holes of the upper and lower flat portions.